The present invention relates to improvements in a steering control system of a wheeled vehicle, and more particularly to a steering control system where a non-linear characteristic of a steering system is treated as a factor in a feedback control.
A Japanese Patent Provisional Publication No. 61-67670 discloses a conventional steering angle control system having a feed-forward compensation section for producing a desired response of a vehicle motion variable and a feedback compensation section for suppressing disturbances.
However, this conventional system has neglected a non-linear characteristic of a steering system which characteristic is that a desired vehicle motion variable is not proportional (linear) to the steering angle of a steering wheel. This non-linear characteristic tends to generate a difference between a desired value and a detected value of a vehicle motion variable even when the vehicle is not influenced by disturbances. This difference functions in the feedback control as if the vehicle is influenced by disturbances, and therefore a driver may feel strange during a turning control.